Obsessive-compulsive disorder (OCD) is a relatively common, often chronic and disabling disorder with high rates of partial and/or absent response to standard, recommended treatments. We report a case of treatment-resistant OCD that was successfully treated with a pharmacological augmentation of lamotrigine plus clomipramine. The patient, a 59-year-old woman, was on a stable dose of clomipramine (225 mg/day) when she was started on lamotrigine (up to 150 mg/day). After 10 weeks of this treatment, her clinical condition remarkably improved, as indicated by a significant decrease of the Yale-Brown Obsessive-Compulsive Scale. This case suggests some preliminary evidence that the addition of glutamatergic agent lamotrigine may be useful in treatment-resistant OCD. However, further controlled studies are needed to support this finding.